Hydration is simultaneously simpler and more nuanced than most runners think.

You don't need to follow complicated formulas. You do need to avoid both extremes.

Here's how to get it right.

Why Hydration Matters

The Role of Fluid

Water in your body:

• Regulates temperature (through sweating)
• Transports nutrients and oxygen
• Lubricates joints
• Removes waste products

During running, you lose water through sweat and respiration.

The Dehydration Effect

The reality: Most runners finish races 2-3% dehydrated. This is normal and tolerable.

The Overhydration Risk

Hyponatremia = dangerously low blood sodium from drinking too much water.

Symptoms:

• Nausea and vomiting
• Headache
• Confusion
• Swelling
• Seizures (severe cases)

Who's at risk:

• Slower runners (more time to drink)
• Smaller runners (less total blood volume)
• Those who drink on a schedule, not by thirst
• Cool, wet conditions (less sweating)

Critical point: Hyponatremia can be more dangerous than dehydration.

How Much to Drink

The Thirst Approach

Current consensus: Drink when you're thirsty.

Your body's thirst mechanism is remarkably accurate. When you need fluid, you feel thirsty.

Old advice (now outdated): "Drink before you're thirsty."

This led to overdrinking, hyponatremia, and unnecessary GI distress.

The Numbers Approach

If you prefer numbers:

General daily intake:

• ~0.5 oz per pound of body weight
• 150 lb person = ~75 oz daily
• Adjust up for heat, training load

During running:

• 4-8 oz every 15-20 minutes (rough guide)
• Actual needs vary enormously by individual

Know Your Sweat Rate

Sweat rate calculation:

1. Weigh yourself before running (in minimal clothing)
2. Run for 1 hour at moderate effort
3. Weigh yourself after (same minimal clothing)
4. Add fluid consumed during run

Formula: Pre-run weight - Post-run weight + fluid consumed = sweat loss

Example:

• Pre: 150 lb
• Post: 148 lb (2 lb loss = 32 oz)
• Drank: 16 oz during run
• Sweat rate: 32 + 16 = 48 oz/hour

Typical range: 16-60+ oz/hour depending on conditions, individual variation.

Factors That Affect Needs

Increased needs:

• Hot weather
• High humidity (sweat doesn't evaporate, body sweats more)
• High intensity
• Altitude
• Larger body size
• Genetic heavy sweaters

Decreased needs:

• Cool weather
• Lower intensity
• Acclimation to heat
• Smaller body size

Before Running

Daily Hydration

Goal: Arrive at runs adequately hydrated.

Signs you're hydrated:

• Pale yellow urine
• Regular urination
• Not feeling thirsty

Signs you're dehydrated:

• Dark yellow urine
• Infrequent urination
• Thirst, headache, fatigue

Pre-Run Hydration

2-4 hours before:

• Drink 16-20 oz of water or sports drink
• Allow time to urinate before running

30 minutes before:

• If still thirsty, drink another 8-12 oz
• Don't force fluids if you're not thirsty

Morning Runs

You wake slightly dehydrated. For early morning runs:

• Drink 8-16 oz upon waking
• Eat a small breakfast if time permits
• Don't over-hydrate trying to compensate

During Running

Short Runs (< 60 minutes)

Hydration needs: Minimal. You won't significantly dehydrate.

Recommendation: Water if you're thirsty. Nothing is fine.

Medium Runs (60-90 minutes)

Hydration needs: Moderate, especially in heat.

Recommendation: Carry water or plan a route with water access. Drink to thirst.

Long Runs (90+ minutes)

Hydration needs: Significant.

Recommendation:

• Plan water stops or carry fluids
• Aim for 4-8 oz every 15-20 minutes (adjust by sweat rate)
• Include electrolytes for very long runs

Carrying Fluids

Options:

• Handheld bottle (10-20 oz)
• Waist belt (multiple small bottles)
• Hydration vest (larger capacity for ultras)
• Route with water fountains

Race Hydration

Aid stations:

• Don't drink at every station if you're not thirsty
• Slow down to drink properly
• Water for short races; sports drink for long ones

Practice: Train your hydration strategy before race day.

After Running

Immediate Post-Run

If you finished mildly dehydrated (normal):

• Drink to thirst in the hour after
• Include sodium with fluids (sports drink or food)

If you finished significantly dehydrated:

• Drink 16-24 oz per pound of body weight lost
• Include electrolytes

Recovery Hydration

Monitor:

• Urine color should return to pale yellow within hours
• If still dark after 2-3 hours, drink more

Include food:

• Food provides water, sodium, and helps retention
• Don't rely only on pure water for rehydration

Electrolytes

Why Electrolytes Matter

Sweat contains:

• Water (mostly)
• Sodium (200-2000+ mg/liter, depending on individual)
• Potassium, magnesium, chloride (smaller amounts)

Sodium is the key electrolyte for runners.

When You Need Electrolytes

Sources of Electrolytes

Sports drinks: Gatorade, Nuun, Skratch (~300-500 mg sodium per 16 oz)

Salt tablets: SaltStick, Base Salt (~200-400 mg per capsule)

Food: Pretzels, crackers, pickles

Gels: Many contain 50-100 mg sodium each

How Much Sodium

General target for long runs: 300-600 mg sodium per hour

Salty sweaters: May need 800-1000+ mg/hour

Know your sweat: White salt residue on clothes/face indicates high sodium loss.

Common Hydration Mistakes

1. Drinking Too Much

The problem: Following outdated "drink before thirsty" advice.

The result: GI distress, sloshing, potential hyponatremia.

The fix: Drink to thirst.

2. Drinking Too Little

The problem: Ignoring thirst during long runs.

The result: Performance decline, potential heat issues.

The fix: If you're thirsty, drink.

3. Water Only for Long Runs

The problem: Hours of sweating with only water replacement.

The result: Diluted sodium, cramping, hyponatremia risk.

The fix: Add electrolytes for runs over 60-90 minutes.

4. New Products on Race Day

The problem: Using race-provided sports drink for the first time.

The result: GI distress at the worst possible time.

The fix: Practice with any product you'll use in racing.

5. Not Knowing Your Sweat Rate

The problem: Guessing fluid needs.

The result: Systematic over- or under-hydrating.

The fix: Calculate your sweat rate in different conditions.

Hydration Myths

"8 Glasses a Day"

Truth: There's no scientific basis for this specific number. Needs vary by individual.

"Clear Urine = Optimal"

Truth: Very clear urine may indicate overhydration. Pale yellow is the goal.

"You Can't Drink Too Much"

Truth: You absolutely can. Overhydration is dangerous.

"Coffee Dehydrates You"

Truth: The mild diuretic effect is more than offset by the fluid in the coffee. Moderate caffeine doesn't cause dehydration.

Hydration doesn't need to be complicated. Drink when you're thirsty, add electrolytes for long or hot runs, and avoid both extremes. Your body's thirst mechanism is more reliable than any formula.

For the complete guide to nutrition for runners, see the Running Nutrition Complete Guide.

Calculate your hydration needs with our Hydration Calculator.